GH-releasing hormone and GH-releasing peptide-6 for diagnostic testing in GH-deficient adults

BACKGROUND

The diagnosis of growth hormone (GH) deficiency in adults is based on provocative testing of GH secretion. The insulin tolerance test (ITT), currently the favoured test for this diagnosis, has been criticised for poor reproducibility and inconvenience. Since the combined administration of GH-releasing hormone (GHRH) plus GH-releasing peptide-6 (GHRP-6) is the most potent stimulus of GH secretion, we did a multicentre study comparing GH peaks elicited by ITT with those elicited by the GHRH/GHRP-6 test in healthy controls and GH-deficient individuals (cases).

METHODS

125 adult patients with organic pituitary disease and 125 healthy individuals were studied. All cases and controls were given GHRH 1 microg per kg bodyweight intravenously plus GHRP-6 1 microg per kg intravenously at 0 min and blood samples were obtained during a subsequent 120 min period. 27 controls and all cases had an ITT. Inclusion criteria were severe GH deficiency--ie, a GH peak after ITT of < or = 3 microg/L. Results of the GHRH/GHRP-6 test were analysed by receiver-operating characteristic curve methodology.

FINDINGS

GH peaks seen after the GHRH/GHRP-6 test did not result in any side-effects and were not affected by age, sex, amount of adipose tissue, or by the GH assay system used. The GH mean peak after the GHRH/GHRP-6 test was 59.2 microg/L (SD 2.2) for controls and 4.1 microg/L (0.3) for cases, whereas after ITT the mean peak was 14.3 microg/L (1.7) and 0.5 microg/L (0.06), respectively. The differential peak responses of controls and cases was greater (p<0.001), for GHRH/GHRP-6 test than for ITT. When individually analysed GH peaks were a continuum, from 139.0 microg/L to 0.01 microg/L, with a cut-off point of 15.0 microg/L. The GHRH/GHRP-6 test performed well under the ROC curve analysis. For clinical utility, it is then proposed that values > or = 20.00 microg/L be considered normal and < or = 10.00 microg/L as GH deficient.

INTERPRETATION

The GHRH/GHRP-6 test is a convenient, safe and reliable test for adult GH deficiency and is not confounded by clinical factors known to alter GH secretory patterns. An evoked GH concentration of > or = 15.0 microg/L accurately distinguishes between healthy and GH-deficient adults.

Hypertensive disorders in pregnancy: screening by uterine artery Doppler imaging and blood pressure at 11-13 weeks

OBJECTIVES

To examine the performance of screening for hypertensive disorders in pregnancy at 11-13 weeks by a combination of the maternal history, uterine artery Doppler imaging and blood pressure.

METHODS

This was a prospective screening study for pre-eclampsia (PE) requiring delivery before 34 weeks (early PE), late PE and gestational hypertension (GH) in women attending for their routine first hospital visit in pregnancy at 11 + 0 to 13 + 6 weeks of gestation. Maternal history was recorded, color flow Doppler imaging was used to identify the uterine artery with the lowest pulsatility index (L-PI) and automated devices were used to measure the mean arterial pressure (MAP). The performance of screening for PE and GH by a combination of the maternal factor-derived a-priori risk, the uterine artery L-PI and MAP was determined.

RESULTS

There were 8061 (96.4%) cases unaffected by PE or GH, 165 (2.0%) that developed PE including 37 that required delivery before 34 weeks (early PE) and 128 with late PE, and 140 (1.7%) that developed GH. The MAP was higher in early PE, late PE and GH than in the unaffected group (P < 0.0001), and in early PE than in GH (P = 0.002). The uterine artery L-PI was significantly higher in early PE and late PE than in the unaffected group (P < 0.0001), in early PE than late PE or GH (P < 0.0001), and in GH than in the unaffected group (P = 0.014). In screening by a combination of the maternal factor-derived a-priori risk, uterine artery L-PI and MAP, the estimated detection rate at a 10% false-positive rate was 89.2% (95% CI, 74.6-96.9%) for early PE, 57.0% (95% CI, 48.0-65.7%) for late PE and 50.0% (95% CI, 41.4-58.6%) for GH.

CONCLUSIONS

Effective screening for hypertensive disorders in pregnancy is provided by a combination of maternal history, uterine artery Doppler imaging and blood pressure at 11-13 weeks.

Ionization chamber dosimetry of small photon fields: a Monte Carlo study on stopping-power ratios for radiosurgery and IMRT beams

Absolute dosimetry with ionization chambers of the narrow photon fields used in stereotactic techniques and IMRT beamlets is constrained by lack of electron equilibrium in the radiation field. It is questionable that stopping-power ratio in dosimetry protocols, obtained for broad photon beams and quasi-electron equilibrium conditions, can be used in the dosimetry of narrow fields while keeping the uncertainty at the same level as for the broad beams used in accelerator calibrations. Monte Carlo simulations have been performed for two 6 MV clinical accelerators (Elekta SL-18 and Siemens Mevatron Primus), equipped with radiosurgery applicators and MLC. Narrow circular and Z-shaped on-axis and off-axis fields, as well as broad IMRT configured beams, have been simulated together with reference 10 x 10 cm2 beams. Phase-space data have been used to generate 3D dose distributions which have been compared satisfactorily with experimental profiles (ion chamber, diodes and film). Photon and electron spectra at various depths in water have been calculated, followed by Spencer-Attix (delta = 10 keV) stopping-power ratio calculations which have been compared to those used in the IAEA TRS-398 code of practice. For water/air and PMMA/air stopping-power ratios, agreements within 0.1% have been obtained for the 10 x 10 cm2 fields. For radiosurgery applicators and narrow MLC beams, the calculated s(w,air) values agree with the reference within +/-0.3%, well within the estimated standard uncertainty of the reference stopping-power ratios (0.5%). Ionization chamber dosimetry of narrow beams at the photon qualities used in this work (6 MV) can therefore be based on stopping-power ratios data in dosimetry protocols. For a modulated 6 MV broad beam used in clinical IMRT, s(w,air) agrees within 0.1% with the value for 10 x 10 cm2, confirming that at low energies IMRT absolute dosimetry can also be based on data for open reference fields. At higher energies (24 MV) the difference in s(w,air) was up to 1.1%, indicating that the use of protocol data for narrow beams in such cases is less accurate than at low energies, and detailed calculations of the dosimetry parameters involved should be performed if similar accuracy to that of 6 MV is sought.

Effects of estrogens on the redox chemistry of iron: a possible mechanism of the antioxidant action of estrogens

The preventive effects of estrogens on FeSO4-induced lipid peroxidation are closely correlated with their inhibition of Fe(II) oxidation during peroxidation. Estrogens affected the redox status of iron in aqueous solution with varying degrees of effectiveness. 2-Hydroxyestradiol substantially decreased the oxidation of Fe(II) and was the most potent Fe(III) reductant. Diethylstilbestrol and 4-hydroxyestradiol also exhibited reduction properties, whereas the phenolic estrogens 17 beta-estradiol, estrone, and 17 alpha-ethynylestradiol displayed slighter or no effects. Present results demonstrate that catecholestrogens and diethylstilbestrol directly alter the iron redox chemistry, this fact probably being involved in the antioxidant effects of these molecules.

Characterization of megavoltage electron beams delivered through a photon multi-leaf collimator (pMLC)

A study is presented that characterizes megavoltage electron beams delivered through an existing double-focused photon multi-leaf collimator (pMLC) using film measurements in a solid water phantom. Machine output stability and linearity were evaluated as well as the effect of source-to-surface distance (SSD) and field size on the penumbra for electron energies between 6 and 18 MeV over an SSD range of 60-100 cm. Penumbra variations as a function of field size, depth of measurement and the influence of the jaws were also studied. Field abutment, field flatness and target coverage for segmented beams were also addressed. The measured field size for electrons transported through the pMLC was the same as that for an x-ray beam up to SSDs of 70 cm. At larger SSD, the lower energy electron fields deviated from the projected field. Penumbra data indicated that 60 cm SSD was the most favourable treatment distance. Backprojection of P(20-80) penumbra data yielded a virtual source position located at 98.9 cm from the surface for 18 MeV electrons. For 6 MeV electrons, the virtual source position was at a distance of 82.6 cm. Penumbra values were smaller for small beam slits and reached a near-constant value for field widths larger than 5 cm. The influence of the jaws had a small effect on the penumbra. The R90 values ranged from 1.4 to 4.8 cm between 6 and 21 MeV as measured at 60 cm SSD for a 9 x 9 cm2 field. Uniformity and penumbra improvement could be demonstrated using weighted abutted fields especially useful for small segments. No detectable electron leakage through the pMLC was observed. Bremsstrahlung measurements taken at 60 cm SSD for a 9 x 9 cm2 field as shaped by the pMLC compared within 1% to bremsstrahlung measurements taken at 100 cm SSD for a 10 x 10 cm2 electron applicator field at 100 cm SSD.

Healthcare resource utilization during 1-year treatment with long-acting, injectable risperidone

BACKGROUND

Schizophrenia is associated with disproportionately high costs, mainly due to hospitalization rates. This study assessed healthcare resource use in patients with schizophrenia and schizoaffective disorder during treatment with long-acting risperidone.

METHODS

Patients (n = 397 [inpatients, 24%; outpatients, 76%]) receiving stable doses of an antipsychotic for >or=4 weeks were eligible to enter this 1-year, open-label study. Following a 2-week run-in period (oral risperidone 1-6 mg/day), patients received intramuscular long-acting risperidone (25 or 50 mg modal dose) every 2 weeks. Healthcare resource use in the previous 12 weeks was assessed at baseline and 12-weekly intervals.

RESULTS

Patients needing hospitalization decreased significantly and continuously from 38% during the 12 weeks before study entry to 12% during the last 12 weeks. Mean hospitalization length during the study was 30.5 days (outpatients, 4.9 days; inpatients, 110 days). This included 28 patients (7%) who remained in hospital throughout the study. During treatment, 71% of those hospitalized at baseline were discharged. Partial hospitalization decreased significantly from 7% of patients during the 12 weeks before treatment to 3% during the last 12 weeks. Outpatient consultations also decreased significantly from 70% of patients to 30% in the first 12 weeks of treatment and remained stable thereafter. Only 9% of patients required an emergency room visit; mostly for non-psychiatric conditions.

CONCLUSION

Healthcare resource use is significantly reduced in patients with stable schizophrenia or schizoaffective disorder receiving long-acting risperidone. It is highly likely that these reductions will decrease healthcare costs in patients receiving long-acting risperidone.

Quality-of-life measurement in patients with inflammatory bowel disease receiving social support

BACKGROUND

Crohn's disease and ulcerative colitis, referred to as inflammatory bowel diseases, affect mainly young adults and have an elevated morbidity and a negative effect on quality of life. This study aimed to compare the health-related quality of life between 2 randomized groups of patients with inflammatory bowel disease: (1) the supported group (SG), patients receiving social support for an 18-month period, and (2) the control group (CG), patients receiving no social support.

METHODS

Health-related quality of life was assessed at 4 moments with the Portuguese versions of the Medical Outcomes Study Short Form 36 and the Inflammatory Bowel Disease Questionnaire (IBDQ), both validated in Brazil.

RESULTS

In the SG, using analysis of variance for repeated measures complemented by the Bonferroni test positive variations were observed (1) in the Social Aspects domain, between the first and third evaluations (P = 0.044), and (2) in the Emotional Aspects domain, between the first and second and the third and fourth evaluations (P = 0.029).

CONCLUSIONS

In the sample studied, social support, measured by use of the Inflammatory Bowel Disease Questionnaire, had a positive impact on the social and emotional aspects of quality of life.

Actions of activins, inhibins and follistatins: implications in anterior pituitary function

1. The anterior pituitary is well documented to be under the control of central and peripheral factors that dynamically interact to affect cell-specific modulation of pituitary functions. However, it is becoming increasingly evident that these extrinsic factors work in concert with a variety of local products that exert autocrine/paracrine control on pituitary cells. 2. These factors modulate the activity of their target pituitary cells by altering the synthesis and secretion of cell-specific hormones and by exerting control on the growth and differentiation of cells of this tissue. Included in the list of growth factors and bioactive peptides known to be products of pituitary cells are the activins, possibly inhibins and follistatins. 3. These protein factors play an important role in the local modulation of several pituitary cell types and are crucial for the maintenance of normal follicle-stimulating hormone production and, thus, reproductive function and fertility.

Evaluative and Discriminative Properties of the Portuguese MacNew Heart Disease Health-related Quality of Life Questionnaire

The aim of this study was to validate the Portuguese version of the self-administered MacNew Heart Disease Health-related Quality of Life (MacNew) questionnaire in patients after diagnosis of acute coronary syndrome. The MacNew, with a Global score and physical, emotional and social subscales, the Short Form SF-36 (SF-36) and the Hospital Anxiety and Depression Scale (HADS) were completed at baseline by 150 patients and again by 48 clinically stable patients 2-3 weeks later. A cohort of 50 different patients completed the same questionnaires before and after a cardiac rehabilitation program in order to examine responsiveness. Acceptance of the MacNew by the patients was good and the three factor model was substantiated and explained 52.2% of the variance. Internal consistency, intra-class-correlation, and test-retest reliability each exceeded 0.72. The predicted construct validity hypotheses were partially confirmed. The discriminative validity of the MacNew was confirmed with significantly higher MacNew scores for patients with normal left ventricular function, with improved health status, and who were not anxious or depressed. Even though MacNew scores improved significantly following cardiac rehabilitation, the evaluative validity of the MacNew was less robust with small responsiveness statistics. The Portuguese version of the MacNew HRQL questionnaire appears to be a reliable, valid, and moderately responsive instrument to evaluate health-related quality of life after diagnosis of acute coronary syndrome.

Relationship of stem water potential and leaf conductance to vegetative growth of young olive trees in a hedgerow orchard

In 2005, four irrigation treatments were applied to a 3-year-old cv. Cornicabra orchard. In T1, wetted soil volume was maintained close to field capacity by irrigating when soil sensors indicated that soil water potential in the root zone had fallen to –0.03 MPa and 0.06 MPa from spring until 15 August and from 15 August until September, respectively. On those days, 8, 6, 4, and 2 h of irrigation was applied to T1, T2, T3, and T4, so that over the season they received 106, 81, 76 and 31 mm of irrigation, respectively. The high value for T3 was the result of a valve failure on 13 June. Measurements were maintained throughout the experimental period of relative extractable water (REW) to 1 m depth at the wetted volume (0.30 m from a drip emitter), shoot length, trunk diameter, stem water potential (Ψstem) and leaf conductance (gl). The irrigation treatment significantly affected REW (P < 0.10), Ψstem, gl and vegetative growth (P < 0.05). Ψstem, and trunk diameter were the least variable parameters and Ψstem and shoot growth were the most sensitive to water stress. Although T1 received 24% more water than T2, no significant differences were detected in vegetative growth. T2 should be considered the optimum irrigation value. The mean monthly Kc for T2 was 0.086. The failure of the valve in T3 simulated a wet spring followed by limited irrigation. Irrigation applied was similar to T2 but shoot growth stopped one month earlier and lower values of Ψstem and gl were observed after mid August. REW was highly related to vegetative growth, 66% of maximum being achieved at REW 0.53 and 50% at 0.45. gl was independant of plant or soil water status and did not determine vegetative growth. A strong relationship established Ψstem as a good indicator of vegetative growth and hence of water stress. Shoot growth was 66% of maximum at Ψstem –1.5 MPa and 50% at –1.8 MPa.

Early hyponatraemia after pituitary surgery: cerebral salt-wasting syndrome

Hyponatraemia is a common complication in patients undergoing neurosurgery. It can be caused either by the syndrome of inappropriate secretion of antidiuretic hormone or by the cerebral salt-wasting syndrome (CSWS). CSWS frequently occurs in patients suffering from subarachnoid haemorrhage and brain injury, but it is rare after pituitary tumour surgery. However, this diagnostic possibility should be considered as these disorders require specific treatment and have different prognoses. In this article, we present a case of acute and early hyponatraemia caused by CSWS after pituitary tumour surgery. We also revise the aetiology, mechanisms, differential diagnosis and treatment of hyponatraemia after pituitary surgery.

Pilot interferon-beta trial in children with chronic hepatitis B who had previously not responded to interferon-alpha therapy

BACKGROUND

Recombinant interferon alpha (IFN-alpha) treatment is useful in 40% of children with chronic hepatitis B. However, nonresponder children continue to have viral replication and a progressive disease.

OBJECTIVE

To administer natural IFN-beta to hepatitis B virus chronic carrier children who had not responded to a previous IFN-alpha cycle.

METHODS

Twenty-two children with chronic hepatitis B, nonresponders to a previous IFN-alpha cycle, were retreated with 5 MU/m2 of body surface of natural IFN-beta, administered intramuscularly, three times per week for 24 weeks.

RESULTS

At the end of treatment, 9 (41%) of 22 children became hepatitis B virus DNA negative. Hepatitis B e antibodies (anti-HBe) developed in 5 of these children, and 6 had normal alanine aminotransferase values. At the end of the posttreatment follow-up (21 months from the beginning of the study), 10 (45%) of 22 children were viral DNA negative, 7 (32%) of 22 were anti-HBe positive (none of them had viral DNA in serum), and 11 (50%) of 22 had normal alanine aminotransferase levels (10 without detectable viral DNA and 7 anti-HBe positive).

CONCLUSION

IFN-beta seems to be an effective retreatment therapy for children with chronic hepatitis B who are nonresponders to a first IFN-alpha cycle; however, a controlled study should be performed to confirm these results.

A single growth hormone (GH) determination is sufficient for the diagnosis of GH-deficiency in adult patients using the growth hormone releasing hormone plus growth hormone releasing peptide-6 test

BACKGROUND

The diagnosis of GH deficiency in adults is based on the provocative testing of GH secretion. When testing a patient with suspected GH deficiency, clinicians assess the whole secretory curve and select the GH peak as an index of secretory capability. This procedure is time consuming and the determination of GH in several samples is necessary. The combined administration of growth hormone releasing hormone (GHRH) plus growth hormone releasing peptide-6 (GHRP-6) is an effective test of GH secretion, and it has been unambiguously demonstrated that the elicited GH peak is capable of segregating normal GH secretion subjects from GH deficient patients on an individual basis. The GHRH + GHRP-6 test biochemically classifies patients into three groups; those with a stimulated GH peak >/= 20 micro g/l are considered normal and those with peaks at </= 10 micro g/l as GH deficient. The group comprising individuals between these parameters is considered uncertain, and the results are further interpreted according to clinical information, or by other tests.

OBJECTIVE

As the GHRH + GHRP-6 test induces GH peaks consistently in the first 30 minutes, the working hypothesis assessed in this study was whether a single determination of GH 30 minutes after stimulus could provide the same clinical classification as the whole secretory curve.

PATIENTS AND METHODS

Three hundred and forty-nine adult subjects (146 patients with organic pituitary disease and 203 healthy subjects) were studied. All were administered GHRH 1 micro g/kg i.v. plus GHRP-6 1 micro g/kg i.v. at 0 minutes, and blood samples were obtained at regular intervals. GH was determined in all samples.

RESULTS

GHRH + GHRP-6-evoked GH peaks in controls and patients were not correlated with GH basal values, making this determination useless for test validation. In contrast, an excellent correlation was observed between GH values at 30 minutes and the GH peaks (r = 0.994, P < 0.0001). When comparing the 30-minute GH values against the peaks, the biochemical classification changed from normal toward uncertain in only five out of 203 control subjects, which is without clinical relevance according to Bayes theorem. Similarly, when the 30-minute value was used instead of the peak in GH deficient patients, only two out of 146 patients moved from the uncertain area toward the GH deficient one. Thus, better diagnostic classification was provided for patients.

CONCLUSIONS

The GHRH + GHRP-6 test is a convenient, safe and reliable, provocative test of GH reserve in adults, which can be reduced to a single fixed GH determination 30 minutes after stimulus.

The change of response of ionization chambers in the penumbra and transmission regions: impact for IMRT verification

Significant deviations from the expected dose have been reported in the absolute dosimetry validation of an intensity modulated radiation therapy treatment when individual segments are analyzed. However, when full treatment is considered and all segment doses are added together, these discrepancies fade out, leading to overall dose deviations below a 5% action level. This contradictory behavior may be caused by a partial compensation between detector over-responding and under-responding for measurement conditions far from radiation equilibrium. We consider three treatment verification scenarios that may lead to ionization chamber miss-responding, namely: narrow beam irradiation, field penumbra location and multi-leaf collimator transmission contribution. In this work we have analyzed the response of three different ionization chambers with different active volume under these conditions by means of Monte Carlo (MC) simulation methods. Correction factors needed to convert the detector readout into actual dose to water were calculated by inserting the specific detector geometry (carefully modeled) into the simulations. This procedure required extensive use of parallel computing resources in order to achieve the desired level of uncertainty in the final results. The analysis of the simulations shows the relative contribution of each of the three previously mentioned miss-responding scenarios. Additionally, we provide some evidence on dose deviation compensation in multi-segment radiotherapy treatment verification.

MCTP system model based on linear programming optimization of apertures obtained from sequencing patient image data maps

PURPOSE

The authors present a hybrid direct multileaf collimator (MLC) aperture optimization model exclusively based on sequencing of patient imaging data to be implemented on a Monte Carlo treatment planning system (MC-TPS) to allow the explicit radiation transport simulation of advanced radiotherapy treatments with optimal results in efficient times for clinical practice.

METHODS

The planning system (called CARMEN) is a full MC-TPS, controlled through aMATLAB interface, which is based on the sequencing of a novel map, called "biophysical" map, which is generated from enhanced image data of patients to achieve a set of segments actually deliverable. In order to reduce the required computation time, the conventional fluence map has been replaced by the biophysical map which is sequenced to provide direct apertures that will later be weighted by means of an optimization algorithm based on linear programming. A ray-casting algorithm throughout the patient CT assembles information about the found structures, the mass thickness crossed, as well as PET values. Data are recorded to generate a biophysical map for each gantry angle. These maps are the input files for a home-made sequencer developed to take into account the interactions of photons and electrons with the MLC. For each linac (Axesse of Elekta and Primus of Siemens) and energy beam studied (6, 9, 12, 15 MeV and 6 MV), phase space files were simulated with the EGSnrc/BEAMnrc code. The dose calculation in patient was carried out with the BEAMDOSE code. This code is a modified version of EGSnrc/DOSXYZnrc able to calculate the beamlet dose in order to combine them with different weights during the optimization process.

RESULTS

Three complex radiotherapy treatments were selected to check the reliability of CARMEN in situations where the MC calculation can offer an added value: A head-and-neck case (Case I) with three targets delineated on PET/CT images and a demanding dose-escalation; a partial breast irradiation case (Case II) solved with photon and electron modulated beams (IMRT + MERT); and a prostatic bed case (Case III) with a pronounced concave-shaped PTV by using volumetric modulated arc therapy. In the three cases, the required target prescription doses and constraints on organs at risk were fulfilled in a short enough time to allow routine clinical implementation. The quality assurance protocol followed to check CARMEN system showed a high agreement with the experimental measurements.

CONCLUSIONS

A Monte Carlo treatment planning model exclusively based on maps performed from patient imaging data has been presented. The sequencing of these maps allows obtaining deliverable apertures which are weighted for modulation under a linear programming formulation. The model is able to solve complex radiotherapy treatments with high accuracy in an efficient computation time.

GODDESS: A Goal-Directed Decision Structuring System

This paper describes an operational version of a computerized, domain-independent, decision support system which is based on a novel, goal-directed structure for representing decision problems. The structure allows the user to state relations among aspects, effects, conditions, and goals, in addition to actions and states which are the basic components of the traditional decision tree approach. The program interacts with the user in a stylized English-like dialogue, starting with the stated objectives and proceeding to unravel the more detailed means by which these objectives can be realized. At any point in time, the program focuses the user's attention on the issues which are most crucial to the problem at hand. The structure used is more compatible with the way people encode knowledge about problems and actions, and therefore promises to offer the following advantages: 1) judgments and beliefs issued by the user constitute a more valid representation of the user's experience; and 2) the user may be guided toward the discovery of action alternatives he otherwise would not have identified.

Dose painting by means of Monte Carlo treatment planning at the voxel level

PURPOSE

To develop a new optimization algorithm to carry out true dose painting by numbers (DPBN) planning based on full Monte Carlo (MC) calculation.

METHODS

Four configurations with different clustering of the voxel values from PET data were proposed. An optimization method at the voxel level under Lineal Programming (LP) formulation was used for an inverse planning and implemented in CARMEN, an in-house Monte Carlo treatment planning system.

RESULTS

Beamlet solutions fulfilled the objectives and did not show significant differences between the different configurations. More differences were observed between the segment solutions. The plan for the dose prescription map without clustering was the better solution.

CONCLUSIONS

LP optimization at voxel level without dose-volume restrictions can carry out true DPBN planning with the MC accuracy.

Role of the new growth hormone-releasing secretagogues in the diagnosis of some hypothalamopituitary pathologies

Growth hormone (GH)-releasing hormone (GHRH) and somatostatin have a dominant role in regulating GH secretion. However, results of studies using the new class of GH secretogogues, particularly GHRP-6, indicate that there may also be other, as yet undefined, hypothalamic mechanisms involved. Studies in adults with hypothalamopituitary disconnection (functional pituitary stalk transection), show GHRP-6-mediated GH release to be completely blocked, indicating a main action at the hypothalamic rather than the pituitary level. The synergistic effect of GHRH plus GHRP-6 administration on GH release seen in normal adults (and virtually unaffected by age, obesity, or sex) is also absent in these patients, providing further support for this conclusion. Studies of the effects of GHRP-6 in children with GH deficiency due to perinatal pituitary stalk transection have produced similar findings. It is suggested that the combined GHRH plus GHRH-6 test should be a promising tool for diagnosing GH deficiency states in both children and adults, and may identify a subgroup of patients with GH deficiency caused by interruption of the hypothalamopituitary connection.

A Monte Carlo approach for small electron beam dosimetry

BACKGROUND AND PURPOSE

In treatments where it is necessary to conform the field shape yielding a very small effective beam area, dosimetry and conventional treatment planning may be inaccurate. The Monte Carlo (MC) method can be an alternative to verify dose calculations. A conjunctival mucosa-associated lymphoid tissues lymphoma is presented, to show the importance of an independent assessment in critical situations.

MATERIALS AND METHODS

In this work, the MC technique has been employed using the program BEAM (based on EGS4 code). Electron beam simulation has been performed and the results have been compared with those obtained with films. The patient dose distribution has been obtained by two methods: the full Monte Carlo (FMC) simulation and a conventional planning system (PLATO).

RESULTS

Concerning dosimetry, some differences have been observed in the comparison of profiles obtained with film and those obtained with the MC method. Moreover, significant differences were found in the patient isodose distribution between both calculation methods.

CONCLUSIONS

The results highlight that, in treatments where small beams are needed, conventional dosimetry and planning systems have some limitations. Therefore, an independent and more accurate assessment, such as MC, would be desirable.